Currently, there are at least four different ways to fabricate a white light source with light emitting diode (LED) technology. For example, the first technique involves utilizing a red LED, a blue LED, and a green LED. The combined output of these LEDs is mixed or combined to create white light. However, this technique can be expensive, in particular when creating a large area white light source, since it involves many groups of at least three LEDs to create the white light.
The second technique involves adhering yellow phosphor granules to a blue LED with an epoxy. As such, part of the blue light output by the LED excites the yellow phosphor causing it to emit a broad range of spectrum covering red and green light that combines with the blue light of the LED to make white light. However, some of the problems associated with this technique are that it has low conversion efficiency at the phosphor granules and the epoxy tends to degrade as it is exposed to the blue light from the blue LED, causing it to become cloudy.
The third technique involves adhering red, green and blue (RGB) phosphor granules to a ultra-violet (UV) LED with an epoxy. As such, the UV light output by the LED excites the RGB phosphor causing them to emit a broad range of spectrum covering red, green and blue light, resulting in the generation of white light. However, some of the problems associated with this technique are that it has, as in the second technique described above, low conversion efficiency at the phosphor granules and the epoxy tends to degrade as it is exposed to the UV light from the UV LED causing it to become cloudy.
The fourth technique involves an effort to try and grow a gallium nitride (GaN) LED structure on a zinc oxide (ZnO) substrate. As such, the blue light output by the GaN LED excites the ZnO substrate, which generates red and green light. When these red and green lights are combined with the original blue light from the GaN LED, it results in white light. However, one of the problems associated with this technique is that it is very difficult to grow a GaN LED on a ZnO substrate without including defects within the GaN LED since the two different materials have very different physical characteristics. It is noted that the defects within the GaN LED can cause it to adversely degrade. Another problem associated with this technique is the fact that the ZnO substrate is currently very expensive to purchase, thereby adversely driving up the cost of the overall product.
Therefore, it is desirable to address one or more of the above issues.